Raster distortion correction



July 8, 1958 P. M. LUFKIN l 2,842,709

EASTER DISTORTION CORRECTION Filed Oct. 13, 1953 2 Sheets-Sheet 2 IOOOOOOOOU- lllllllllllllm INI/EN TOR.

l! TTORNE Y p Application'ctober 13, 1953, Serial No.,385,746V

' without impairing the focus of the image.

Y 2,842,709 Y RAsTER DIsToRTIoN VcoluutcTIoN Paul: M. Lufkin, Mount Ephraim, N .'J., assignor to'Radio Corporation of America, .a corporation of Delaware Claims. (Cl.Y 315-24) .This invention relates to television deflection systems and more particularly to circuits for correction of raster distortion in cathode ray tubes.

, vIn' present television practice, the image is formed :in a cathode ray tube, or kinescope, Vby an electron beam which is ymagnetically deflected by the windingsrv of the Ydeflection yoke' to trace successive lines of a raster upon auorescent screen. The fluorescent screen is deposited onvthe face plate of. the kinescopewhichis relatively at. rate, the Vraster. which isA therebytraced will be distorted If the electron beam scans at auniform angular Vbecause' the fiat yface plate causes avariance in the length ofthe electron beam as it scans from the centerV to the I edges of the screens,y A uniform rate of angular deflection .will resultin Ya non-uniform trace of the beamV as it sweeps across' the face plate; v I: This` type of raster distortion, known inethe art' as pincushioning, tends to be more pronounced inkine-V scopes with larger flat screen or screens -having a radius of curvature greater than the distance between the beam deflection center and the screen center. `One method of correcting for pincushion distortion'is. to carefully'designV the deflection windings to introduce nonlinear char- 'acteristicsA which will tend to compensate for the nonlinearity of pincushioning. The difficulty experienced with this type of correcting means is that the edges of Y the image are thrown somewhat out of focus, and a vcrom-` promise must be made between a-good vfocus and a good raster shape.

`.lt is an object of this invention, therefore, to provide means Vfor. correcting pincushion distortionV of the raster LA further object is to provide means for such acor- Yrectionwhich may beadjusted subsequently to the assembling of a television receiver or the like.

. A'furtler object is to combinea circuit for correction of raster distortion withA a means for controlling the width ofthe raster. 1 .f I

According to this invention a saturable reactor is used t vary the impedance of the horizontal deflection circuit at the raster repetition frequency. The horizontal deflection is attenuated near the top and bottom of the raster,

' while thecenter of the raster remains relatively unaffected.

' a cathode ray tube television receiving system'inclurding a deflection circuit involving the present invention; Y

Figure 2 is a circuit diagram, partially schematic, of

a second embodiment of this inventionin which the correct'ionvoltage is obtained from the vertical deflection circuit; andV v(TU-nite;i States Patent() h l CC Figure 3 shows the effectV of pincushion distortion upon.

the raster shape and the electivecorrectionwhichfis possible by the use of this inventiornr-`n YIn the various'gures of the drawing similar elements are designated bythesame numeral. u 7'" Referring again, but in more detail, to Figurel" there is shown acircuit arrangement ofa television signal ,Y

receiving and displaying set Vwhich includes an antenna 11 and a television receiver 13 whichincludes'the RTF. section, converter section, I. F. ampliieranddetector. A'sound channel is Vindicated .by the speaker symbol 15. The videoainplier 17 receives a' composite Vsignal fromV which signals are conveyed to the kinescopeV 19and` the sync separatonzl;` The "sync 4separator provides a synchronizing signal for both the horizontal detiection wave. generator Z3 and a vertical deflection crcuitiZS..

r The sawtooth deflection waves from thehorizontal deflec-A 33. The-.damper tube is connectedV to-theB-l-'ip owei'` source through `a linearity control 35.

The horizontal windingsl of the deflection "yoke are coupled to'thevhorizontal output transformer29 at* Points X-X with the impedance winding 37 ofthe saturable reactor 379. The saturation o`r control winding.411 of the saturable reactor 39 is connected to an alternating current source which includes a variac 43 for varying the amplitude of the wave Vas it is applied to a power transformer 45. The output of the power transformer is fed to the saturation winding 41'through a phase control which consists of a variable resistor 47 and condenser`49. The alternating current circuit is completed'through .a bias control which includes a variable resistor 50y and a condenser 51, which are connected to alternating-current ground through the B|` of the power supply. i The saturable reactor -39 is essentially of the. type described in an article entitled, Magnetic Amplifiers by Siegfried R. Hoh published'in the May, 1953 .issue of Tele-Tech, a periodical of Caldwell-Clement, Inc. .The impedance of winding A37is controlled by the degree of saturation of magnetic core material which .depends on the amount of current flow in 'the control winding`41;

The control winding receives both direct current and 60 cycle alternating current. varied .by adjusting the variable reSiStanceSQ-this provides a control for raster width since thedeection'waves will all be uniformly attenuated by a constant impedance in winding 37 resulting from D. C. in the control Winding 41. The alternating current may be varied both in ampli-v tude and in phasethis provides a pincushioning'control, since certain deflection waves will be more attenuated thansgthers by the varying impedance resulting in wind-V ing Y .f

In Figure 2, the circuit is arranged'suchthat the' saturable reactor 39 receives its control signal fromtheY vertical dellection circuit.- The vertical deflection wave generator r52 supplies sawtooth deflection waves to ,the .Y

vertical output tube 53 and thence to the verticalfoutput' transformer 55. The vertical deection windings of the yoke arelconnected to the vertical output transformer at connections Y-Y. The cathode of theV vertical output tube 53 is connected toground through a linearity control which comprises a variable resistor 57 in series with a fixed resistor. 59. and .a shunting capacitor. k61. The cusped or parabolicwave which appears atVV the cathode of the vertical output tube is Ytaken from kthe potential dividing resistor V63 and supplied tothel grid;

2,842,709 i .Patented July. .55.15.2.55 i

The direct current may be' l of the triode amplifyingA tube 65. Resistor 63 must be of considerably greater value than the combination of resistors 57 and 59 in order that the cathode cir-cuit of thevertical output' tube 53 will not be unduly loaded. Itfis therefore usually necessary that the correction wave obtained from the vertical output. cathode be amplified by the triode 65. This` amplified correction wave is applied directly to the control winding 4l of the saturable reactor 39. Width control in this arrangement is achieved by controlling the direct current flow through the. control winding as in the embodiment of Figure 1. This currentcontrol is performed by the resistor means comprising the resistor 67 andthe variable resistor 69. Asin the circuit of Figure 1, the impedance winding 37 of this saturable reactor is included in series with the horizontal deflection winding.

The effect of pincushioning is shown by Figure 3 wherein the heavy outline 67 indicates the shape of a distorted'raster. With the use of this inventionV the horizontal deflection. waves may be attentuated at the beginning and at the end of each vertical scanning sweep, while the horizontal deflection waves are permitted to flow without attenuation when the vertical deflection is` near its mid-point. This has the effect of compressing the raster horizontally at the top and bottom, while permitting essentially the same horizontal dimension in the center of the raster. The sides of the raster can thus ybte-straightened vertically as indicated by the dashed lines 69. This correction in the shape of the raster does not impair the focus of the electron beam at any point on the raster.

In ay system of raster scanning wherein lines or elementary areas of a field are interlaced with other lines or elementary areas of subsequent fields the control vo1tage for pincushion correction must alternate at the frequency of and must be synchronized with the frequency of scanning successive field. The term raster repetition rate as it is used in this specification shall refer to the rate at which the fields of av raster are repeated.

In present television practice a raster is scanned at the rate of 60 fields per second which interlace to yield 30. complete frames per second. The top to 4bottom repetition rate of raster scanning is 60 cycles per second which is the same frequency commonly used in the Western hemispheres for power distribution and public consumption. If a received television signal is in synchronism with the power source of the receiver, then thisv invention may be practiced in the form shown by Figure l. But should the received television signal be at variance with synchronism of the local power source, itl willf be necessary to use a circuit, such as the one in Figure 2, to insure thatV the control current for the saturable reactor 39 remains synchronized with the raster repetition frequency.

What is claimed is:

1. An electron beam deflection system for a television receiver, including an impedance element across which a` deflection wave of frequency equal to the line frequency is presented and a deflection yoke winding, a circuit for correcting pin-cushion distortion of the raster formed in response to applicationof the deflection wave across said impedance element to said deflection yoke winding comprising, a saturable reactor having an impedance winding and a control winding, means coupling said impedance winding and said deflection yoke winding in series across said impedance element, means operatively coupled to said control winding for applying direct current potential thereto, a wave generating circuit producing a cusped wave of frequency equalv to the field frequency, and means to couple said wave generating circuit to said control winding to apply said cusped wave thereto to vary the deflection systemY impedance to correct for said pin-cushion distortion.

2. An electron beam deflection system for a television receiver comprising an impedance element across which a deflection wave frequency equal to the line frequency is developed, a deflection yoke Winding, a circuit for correcting pin-cushion distortion of the raster formed in response to application of the deflection wave across said impedance element to said deflection yoke winding comprising a saturable reactor having an impedance winding and a control winding, means coupling said impedance Winding and saidV deflection yoke winding in series across said impedance element, means operatively coupled to said control winding for applying a direct current potential thereto, a parabolic wave generating circuit producing a parabolic wave of frequency equal to the field frequency, and means to couple said wave generating circuit to said control winding to apply said parabolic wave thereto to vary the deflection system impedance to correct for said pin-cushion distortion.

3. A dellection circuit arrangement for a television receiving set comprising a deflection yoke winding, a deflection wave. generating circuit having a Winding across which the deflection wave is. developed, means including the impedance. winding of a' saturable reactor to couple said deflection yoke' winding across said deflection wave llection wave generating circuit having a winding across which the deflection wave is developed, means including the impedance winding of a saturable reactor to couple said deflection yoke winding across said deflec-V tion wave winding, a control winding on said saturable reactor, a cusped W-ave generating circuit, an amplifying device having an input circuit connected to said cusped wave generating circuit for applying said cusped wave thereto and an output circuit connected to said control winding of said saturable reactor, and adjustable resistance means connecting said control winding of said saturable reactor across a source of direct operating po'- tential to adjust' the direct current passing through said control winding.

5. A deection circuit arrangement for a television receiving set comprising `a horizontal decction yoke winding, a horizontal deflection wave generating circuit having a winding across which the deflection wave is developed, means includingV an impedance winding of a saturable reactor to couple said horizontal deflection yoke winding across said deflection wave winding, a control winding on said saturable reactor, a vertical deection wave generating circuit including an electron discharge device having an anodev and control and cathode electrodes, aresistance element and a capacitance element in parallel between the cathode electrode and a point of fixed referencev potential, means to apply a vertical deilection signal between the control and cathode electrodes thereby to produce a cusped wave across said resistance element, an amplifying devicev having an input circuit connected tol said cathode electrode and an output circuit connected to one-terminal of said control winding of said saturable reactor, means connectingV the other terminal of said control winding of Vsaid saturable reactor to a point of direct operating potential, and an adjustable resistor connected between said one terminal of said control winding and said point of fixed reference potential to adjust thedirect current passing through said control winding.

6. A deflection circuit arrangement for la television receivingset Ycomprising a horizontal deflection yoke winding, a horizontal deflection wave generating circuit'having a winding across which the dellection wave is developed, =a capacitor andv the vimpedance winding ofva assegno,

saturable reactor couplingsaid horizontal ldellection yoke wave generating circuit including an amplifier,tubejrhaving an anode and control-and cathode electrodes, means to apply a vertical deflection signal between;the control.

and cathode electrodes, avariable resistance element and a capacitance element in parallel between the cathode electrodetand ground, a variably tapped resistor connected between said cathode electrode vand' ground, a parabolicwave amplifying tube yhaving a cathode, a grid andan anode, a resistance device between the cathode of' said parabolic wave amplifying tube and ground, a

connection-between said vgrid and the tapping on said variably tapped resistor, and said anode being connected f tovsaid control winding of said saturable reactor, means connecting said Ycontrolwinding of said saturable reactor to a point of direct operating potential, anda further adjustable resistor connected between the anode of said parabolic wave amplifying tube andground to adjust the direct current passingthrough said control winding. Y

7. An electron beam deection system comprising an impedance element across which a deection wave is developed, a deection yoke winding, a saturable reactor having an impedance winding and a control winding,'means` coupling said impedance winding and said ,deflectionryoke winding across said impedance element,

means coupling said control winding to a source of alv ternating current potential, and means coupling a source of direct current potential to said control Winding.

8.V The structure as recited in claim 7 wherein said means coupling said alternating current potential to said control winding comprises means for Yconnecting said next-to-last named coupling meansto apower line, and

" Vmeans are provided for controlling the phase of said alternating current potential applied to said control winding.

9. vAn electron beam deection system for a television receiver comprising: an impedance element across which a deection wave is developed; a deecti-on yoke winding; a circuit for correcting pin-cushion distortion of the raster'formed in response to application of the deflection wave across said impedance element to said deection yoke winding including saiddetlection yoke wind-V ing anda saturable reactor having a control winding and an impedance winding; means coupling said irnped- Vance winding and said deilection yoke winding in series across said impedance element; means for applying a direct current potential Yacross said control winding; means forrdeveloping an alternating current potential;

' means coupling said alternating current developing means `to said control winding for applying said alternating current potential thereto to vary the deection system impedance to correct for said pin-cushion distortion.

10. A deflection control system for a cathode ray beam device comprising: means for producing a plurality of periodically recurring deection signal waves; means responsive to said deflection signal waves for positioning the beam in said cathode ray beam device; means coupling said source of deflection signal waves to said beam positioning means to produce periodic scanning of said beam in said device;a saturable reactor having an impedance winding and a control winding, said control winding being responsive to an Vapplied potential toY vary ythe impedance of said impedance'winding in ac-YV cordance with the magnitude of said potential; a source of said potential; means coupling said impedancewinding to said positioning means in Va current controlling relation thereto; and means operatively coupling said po- .tential source to said control ,winding for applying said potential to said control winding thereby to modify the sponsive-gto said deflection wavesfor positioning` the beam in said cathode ray device; means couplingsaid deile'ctionj wave producing means to Vsaid beam positioning ,means to produce periodic scanning of saidbeam in Vsaid cathode ray device; a saturable reactorhaltving van A impedance Y Winding and a control windiugLsaid control winding being responsive to an alternating current potential lto vary the impedance of said impedance winding in lzic-, cordance with an applied alternating current control signal; means couplingV said impedance windingto lsaid beamV positioning means in such manner that changes in said impedance will produce corresponding changes in the magnitude of one of said dellection Wavespplied to said beam positioning means; means for developing an alternating current control signal having a predetermined waveform; and means Yoperatively coupling said control signal developing means to said control Awinding for applying said control signal to said control winding thereby to modify the beam position inrsaid cathode rayy device in accordance with said control signal.

l2. The subject matter as recited in claim l1 in which said alternating current control signal has a predetermined periodically recurring waveform of the same frequency as said vertical deflection waves thereby to provide dynamic control of said beam deection. Y

13. Dynamic raster distortion compensation apparatus for electron beam deilection systems comprising: a cathode ray display device having a light-producing target and for producing an alternating current control signal having Y a predetermined repetition rate equal to said raster repetition rate; means coupling said control signal producing means to said control signal responsive means for\ap plying said control signal thereto, whereby said beam decction is modiied in said complementary manner thereby to compensate for said raster shape distortion.

14. Dynamic deflection control apparatus for electron beam deflection systems comprising: a cathode ray dis,- play device having a target and means forming and directing an electron beam directed toward said target; electron beam deflecting means coupled to said display device for deflecting said beam in two dimensions; a

saturable reactor having an impedance winding and aVY control winding, said control winding being responsive to a control signal applied thereto to control themagnitude of impedance of said impedance Winding in accordance' with the magnitude of said control signal; means coupling said impedance winding to said electron beam dellecting Y having a predetermined waveform occurringY in synchro-V beam position in said cathode ray beam device in ac- Y cordance with said potential.

nism with the deflection in said other dimension thereby to dynamically modify the deflection in said one dimension, and means coupling said control signal producing means to said control winding.

15. Dynamic deilection control apparatus for electron beam deilection systems comprising: a cathode ray display device having a target and means forming and directing an electron beam toward said target; Vhorizontal agsczivoa 7 and verticall beam detlecting means coupled tosaid display device for deflecting said electron beamV in horii Zontal and vertical directions toY scan a raster on said target, saidde'ecting'means including means for producing horizontalandvertical deflection potentialshaving predetermined periodically recurring repetitionrates and meansapplying said deection potentials to said beam deecting means; a saturable reactor having a control winding and an' impedance winding, said controll winding being responsive to` a` control signal applied thereto to control the` magnitude' of impedance of said impedance Winding in accordance with the magnitude of said control signal; means coupling said impedance winding to said horizontal deflecting means in a current-controlling relationY thereby to control the horizontal deflection ofI said electron' beam in accordance with said control signal;

means forY producing: said control signal, said control' signal including a1 direct curent component for controlling ection potential thereby` to dynamically modify said rasterwidth atV said vertical deection scanning rate, and

means' forv coupling said' control signal producing means to" said control winding.

References Cited inthe le of this patent UNITED STATES PATENTS 2,534,557 Ostreicher Dec. 19, 1950 2,586,395 Flaylor Feb. 19, 1952 2,646,531 Giacoletto July 21, 1953 

